Field of the Invention
The present invention relates generally to systems and methods for separating soil from water, and particularly to such systems employed in agriculture for processing soiled water that is generated as a byproduct of cleaning harvested crops such as tuberous vegetables or other applications where soiled water contains large quantities of relatively heavy suspended solids.
Description of Related Art
About three weeks prior to harvest, potato fields are maintained at maximum saturated water conditions, which has the effect of producing larger potatoes for harvest. It also produces mud and dirt clods, so that when the potatoes are dug from the ground using a draper digging chain, a significant amount of mud and stones are collected along with the potatoes. This unwanted debris is transported along with the harvested crop, and must be eventually removed through further processing. Similar problems occur in any root crop harvest.
A number of methods and apparatus exist in the prior art for removing dirt from products mined or harvested from the earth, such as potatoes and like tuberous plants. Generally, these methods wash dirt from the product by immersion in flowing water or by subjecting the product to a pressurized water spray in a wash compartment or as it moves along a flow channel or conveyor belt. These methods create large volumes of dirty water as a byproduct that must be subjected to further treatment to recycle a portion of the water for use in the upstream washing process, or to clarify the water before returning it to its source or introducing it into a municipal wastewater stream. Known methods for large-scale clarification of water include the use of gravity to collect dirt at the bottom of a settling tank, and the use of centrifugal force to separate dirt and other solids at a flow perimeter. One persistent problem that is largely unaddressed by these methods is how to efficiently dispose of sludge that accumulates in the settling tank or other areas of the clarifying system.
For example, settling tank systems for clarifying wastewater are known to include inner sides converging to a partition through which mud and large particles accumulate by gravity. Conveyance means such as a chain of perforated buckets have been proposed that pass through the well to collect the mud and release water during ascent, eventually dumping the mud into a forgotten pile when the buckets turn over. These systems equip the settling tank with openings through which the tank must be periodically emptied and drained, or manholes through which the tank may be entered for manual cleaning. These are messy, time-consuming tasks, and no solution is provided for removing the dumped mud.
Another system proposes a sedimentation tank equipped with a trough running around its upper perimeter. Dirty water from a revolving drum of a potato washer enters the trough, which has overflow drains at different vertical levels that allow cleaner water to drain into the tank while heavier sediment settles in the trough. The cleaner water is recirculated to the drum; however, the trough must be periodically cleaned by manually scraping out the slurry and muddy sediment, and the tank must also be manually flushed through a special opening provided for that purpose.
Another system proposes to reclaim water used to clean vegetables in a multi-stage spraying process. A first stage sprays off the majority of dirt and directs the resulting dirty water away from the system. A second stage subjects the vegetables to further spray recirculated through a settling tank. A third stage sprays the vegetables with fresh water that replenishes the settling tank. The settling tank has multiple sections separated by vertical baffles, each baffle allowing overflow into a succeeding section so that the cleanest water accumulates in the section furthest from the inlet while sediment accumulates in the bottom of the tank. Second-stage water is recirculated from the furthest section of the tank. Plugs are provided at the bottom of each tank section to facilitate an inefficient, labor-intensive manual removal of accumulated sludge. No solution is provided for clarifying wastewater generated by the first stage.
Another washing system with the help of gravity directs potatoes through a sloped serpentine flume to mechanically loosen and remove dirt prior to spraying. The system produces a muddy waste stream that must be routed to a specialized filtration system for further processing. The system suffers an inherent inefficiency, because the waste stream must be kept sufficiently fluid to entrain solids and prevent muddy buildup, criteria that is contrary to the objective of separating water from soil.
Dishwashing apparatus address a similar problem. In one such exemplary system, the dishwasher circulates water through rotary sprayers to remove food particles and soil. These particles become entrained in the water and are centrifugally separated by action of a separator and collected in an accumulator while the water is recirculated. To drain the dishwasher, a valve is opened to flush the contents of the accumulator through the main drain. Due to relatively high power consumption, and because it ultimately recombines the soil and water, the system is not suitable for clarifying water in a large-scale harvesting process.
More recent systems in this field utilize gravity and centrifugal action of water. These systems propose loading a root crop into a conical separator which directs the crop and overflow water to a rotatable washing drum. Water exiting the drum is pumped back into the separator with sufficient force to support the crop and loosen mud and other debris that fall by force of gravity toward a waste outlet at the bottom, or alternatively, the drum is provided with perforations for filtering out dirt and other particles and entraining them in an auxiliary flow. While these systems clarify the soiled water to some degree, an efficient means for disposing of the collected soil is largely unaddressed. One system proposes a conveyor that runs beneath the waste outlet; however, the collected debris is simply dumped into a pile at a far end of the apparatus, and no solution is provided for replenishing the trough with water to replace significant volumes lost through the waste outlet along with the solid debris. Another of these systems proposes a multi-celled wheel that collects waste slurry from the drum into the cells. The system rotates the wheel in response to sensing an increased cell density so that cells containing the densest slurry are positioned for discharging their contents; however, no means is provided to effect the discharge.
What is needed is an automated and efficient water clarification system scalable for a large harvesting operation that removes concentrated soil from wash water without generating slurry as a byproduct. Although the present invention was originally developed in the context of removing soil and other suspended solids from waste water in the context of food processing, it should be apparent to those skilled in the art that the below described and claimed invention can be used for other applications as well.